Re: Polyimide ablation using excimer laser


"Fred Chen" <flipsu5@xxxxxxxxxxx> wrote in message
news:1114494270.698163.134330@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> bmajeed@xxxxxxxxxx wrote:
>> Hi, I am using 193nm excimer laser to release my devices made from
>> copper and polyimide on a 4-inch quartz wafer. For my experiment I
> need
>> to release a full wafer of only polyimide and then polyimide with
>> copper. I have released polyimide with no problem but when I have
>> copper, the polyimide doesn't seems to be ablating at the fluence at
>> which it ablated before. If I increase the fluence i do get the
>> ablation but it is leaving ablation marks on copper, which I don't
>> want.
>> I have looked through a lot of paper and searched the net but haven't
>> found any reasonable cause for this phenomenon. I would appreciate if
>> someone can help me in this regard.
>>
>> Regards
>
> Just a guess, maybe when the copper is present it draws away heat so
> that the photothermal ablation of the polyimide is not as effective.
>

Here is another guess: Copper is very non-reflective in the UV. Perhaps you
had more reflection from the polyimide/fused quartz interface than from the
polyimide/copper interface. A higher reflectance would increase the
exposure in the polyimide. If you know the n and k for these materials at
193nm you could calculate the reflectances.

--
Adam Norton

Norton Engineered Optics
Optical design and systems engineering for Silicon Valley and beyond.
http://home.ix.netcom.com/~anorton/

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